In a cutting tool, for example, an end mill cutting tool, it has been observed that a high stress area exists in the corner of the insert pocket at the stress relief when it is intersected by a radius.
Cutting tools, such as milling cutters, are rotatable tools of cylindrical, conical, shaped or disk form, having a plurality of cutting edges. Such cutters are available in many forms, such as plain cylindrical, side milling cutters, face and end mills, formed cutters, and standard and special shaped profile cutters.
End mills employing cutting inserts mounted at the front end of the tool are known in the art. The end mills can be used in several types of applications depending on the configuration of the cutting inserts mounted therein. The cutting inserts may present a peripheral cutting edge for side milling, a front cutting edge for face milling and a curved cutting edge of a so-called “ball-nose” end mill for various copying applications. Four flute mills are probably the most common, but 2, 3 or 6 flutes are also used extensively. End mills are in much used because they can execute a wide variety of milling operations, and the initial cost of the cutter is moderate. Shapes other than cylindrical are also in common use. The shank can be parallel or tapered, and need not necessarily be equal to the cutter teeth diameter.
Usually when an end mill is in operation, the machining force is exerted against one edge of the cutter. The resulting moment is resisted by the tool holder which rigidly grips the cutter shank. Ignoring the fact that the direction of the moment changes continually as the cutter revolves, the cutter can be considered to be stressed as a cantilever.
As shown in FIG. 6, a cutting tool 100, such as an end mill, includes a tool body 114 including a top surface 134, an insert receiving pocket 122 with a threaded bore 138, a side wall 126 and a stress relief groove 124 therebetween. Measurements have shown that a maximum equivalent stress of approximately 1.063×e5 psi is located at an area of the stress relief groove 124 adjacent the top surface 134.
While the matter of stress discussed above is related to avoiding tool breakage, no less important is the requirement to minimize tool deflection, in order to improve accuracy and surface finish and to reduce vibration and noise. A constant diameter core results in more tool deflection than necessary, because the high bending moment close to the tool holder, and also near the ends of the tooth flutes nearest the cutter shank, results in bending of the cutter as a result of machining forces. The resultant cutter deflection at the cutting edge would be reduced if the tool steel comprising the cutter core were distributed in a better manner, that is more metal were allocated to the sections under greater stress, at the expense of the more lightly stressed toothed end of the cutter.
Accordingly, there is a need for an improved cutting tool that can overcome the limitations of the known cutting tool, and reduce or eliminate the overall stress of the cutting tool.